Energy harvesting is a process of taking energy from a chaotic system and converting it to a form of energy that can either be stored or used in a controlled manner. Energy harvesting is well known in forms such as hydroelectric turbines, solar cells, wind turbines, and other similar systems that have gained wide public exposure. These large systems harvest relatively large amounts of energy. Recently, science has begun to look for smaller energy harvesting systems. As the power requirements of small electronic devices have decreased, attempts have been made to harvest energy on a smaller scale and use that energy to power the devices.
Many of these micro energy harvesting systems exploit mechanical energy and are based around MEMS or micro-machined, fabricated capacitor electrodes. The initial charging of the capacitor is provided by using an external voltage supply or an electret material, a material which has a built in electric field (i.e. the analogue of a permanent magnet). The means used to subsequently change the capacitance and harvest energy varies among systems. For example, in the case of inertial energy harvesters, mechanical motion of the system moves a mass such that the inertia of the mass is harvested and used to increase the capacitance of the system.
There are two main problems associated with these devices. First, these movable mechanical parts are known to be a major source of failure in these devices due to crack formation, beam break, sticking or other mechanical problems caused by the stress. Second, due to existing infrastructure, the MEMS are often fabricated in silicon therefore causing an inertial mass system to be limited in efficiency by the density of silicon.